Mobile devices are commercially used. Mobile devices such as smartphones, personal assistant devices, and tablet computers have a highly sophisticated display function. The mobile devices can display a color image. As a method used to display a color image, field sequential drive is known. In this drive method, a single frame period is divided into, for example, three periods of a red display period, green display period, and blue display period (or may be referred to as three fields). Corresponding to the three fields, pixels selected for red display, pixels selected for green display, and pixels selected for blue display are driven.
On the other hand, as a white light source applicable to display devices such as liquid crystal display devices, there is a light emitting device including a blue light emitting diode which emits blue light, ultraviolet light emitting diode which emits ultraviolet light, red phosphor which is excited by the ultraviolet light emitted from the lower surface of the ultraviolet light emitting diode to emit red light, and green phosphor which is excited by the ultraviolet light emitted from the upper surface of the ultraviolet light emitting diode. In such a light emitting device, the blue light emitting diode and the ultraviolet light emitting diode are electrically connected to maintain the balance of the mixture of red light from the red phosphor, green light from the green phosphor, and blue light from the blue light emitting diode. In such a light emitting device which essentially emits white light, the blue light emitting diode and the ultraviolet light emitting diode must emit the light at the same time, and it may cause excessive power consumption.
As another white light source, there is a light emitting device including a red light emitting diode, green light emitting diode, and blue light emitting diode arranged linearly, in which the light from two or more light emitting diodes is mixed in a lightguide plate. However, in such a device, the light does not mix sufficiently in the proximity of the incident surface of the lightguide plate and the color may become vague. Such vague color will deteriorate the display quality of the display device.